This invention relates to a method and device for determining the rheological parameters of a flowing fluid, in particular of a suspension or an emulsion.
Similar methods and devices are already known. The ultrasound Doppler method is here used to determine a local velocity profile perpendicular to a line for the fluid that flows through a flow channel and carries suspended or emulsified particles. In addition, the static pressure is measured upstream and downstream from the area of the determined local velocity profile to determine a pressure difference along the direction of flow in the area of the local velocity profile. The velocity profile and the associated pressure difference profile can then be used to determine specific rheological parameters of the examined flowing fluid, e.g., the viscosity function (shear viscosity), yield point, etc.
This combination of ultrasound Doppler method (UVP, ultrasound velocity profiling) and pressure difference determination (PD, pressure difference), referred to by experts as UVP-PD for short, has been described in numerous publications in different variants, always with slight modifications.
The article “Velocity profile measurement by ultrasound Doppler shift method” by Y. Takeda in the International Journal of Heat and Fluid Flow”, Vol. 7, No. 4, December 1986, confirms the suitability of the UVP method for determining a one-dimensional velocity profile in tubules or blood vessels only several millimeters in diameter.
The “Rheological Study of Non-Newtonian Fluids” by E. Windhab, B. Ouriev, T. Wagner and M. Drost, 1.sup.st International Symposium on Ultrasonic Doppler Methods for Fluid Mechanics and Fluid Engineering, September 1996 describes the aforementioned UWP-PD method.
“Ultrasound Doppler Based In-Line Rheometry of Highly Concentrated Suspensions” by B. Ouriev, Diss. ETH No. 13523, Zurich 2000, contains an extensive description of the theoretical and equipment-related principles of the UVP-PD method along with its application in drag shear flows and pressure shear flows, in particular of model suspensions or given rheological fluids, e.g., during the manufacture of chocolate or pasta products. This publication deals with both laminar and turbulent flows.
The UVP-PD method described here yields good results for different kinds of velocity profiles and for the rheological parameters to be determined for the examined fluids. However, the two spaced apart measuring points are always required for measuring the pressure upstream and downstream from the determined velocity profile. While use can today be made of slightly intrusive miniaturized ultrasound transceivers, ultrasound measuring transducers and pressure sensors, the distance between the two pressure measuring points always required upstream and downstream from the acquired local velocity profile for reasons of measuring accuracy already places limits on a further “compacting” of the UVP-PD measuring device by edging the two pressure sensors together.